The Individualization Fallacy in Forensic Science Evidence

Vanderbilt Law Review, Vol 61, No. 1, pp. 199-219, 2008

21 Pages Posted: 10 Jul 2009 Last revised: 29 Dec 2015

Michael J. Saks

Arizona State University (ASU) - Sandra Day O'Connor College of Law

Jonathan J. Koehler

Northwestern University - Pritzker School of Law

Date Written: 2008

Abstract

Forensic identification science involves two fundamental steps. The first step is to compare a questioned item of evidence to an exemplar from a known source and judge whether they appear so alike that they can be said to match. The second step is to assess the meaning of that reported match: What is the probability that the questioned and the known originated from the same source? Part II of this Essay explains what we mean by the term 'individualization fallacy' and describes the origins of individualization in criminalistics. Part III critically examines the arguments offered in support of the individualization hypothesis. This Part also addresses the second step in forensic identification: What inferences can be drawn from a forensic scientist's conclusion that an exemplar (such as a partial fingerprint, handwriting sample, or tireprint) matches a known source? Forensic scientists across a broad array of sub-specialties long have maintained that such a finding is synonymous with a conclusion that the exemplar marking is produced by the known source. Part IV gives a historical account of scientists who have recognized the problem of individualization in forensic science. Part V offers suggestions for ways to improve the scientific foundation of identification in criminalistics. Finally, Part VI concludes that forensic scientists must provide sound evidence for their conclusions and should avoid exaggerating their results.

Keywords: Individualized fallacy, criminalistics, forensic identification

Suggested Citation

Saks, Michael J. and Koehler, Jonathan J., The Individualization Fallacy in Forensic Science Evidence (2008). Vanderbilt Law Review, Vol 61, No. 1, pp. 199-219, 2008. Available at SSRN: https://ssrn.com/abstract=1432516

Michael J. Saks (Contact Author)

Arizona State University (ASU) - Sandra Day O'Connor College of Law ( email )

Box 877906
Tempe, AZ 85287-7906
United States

Jonathan J. Koehler

Northwestern University - Pritzker School of Law ( email )

375 E. Chicago Ave
Chicago, IL 60611
United States

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